Class DefaultHighlighter

This is an adapted version of the FulltextHighlighter posted in
issue: LUCENE-644.

Important: for this highlighter to function properly, field must be stored
with token offsets. Use Field constructor Field(String, String, Field.Store, Field.Index, Field.TermVector) where the
last argument is either Field.TermVector#WITH_POSITIONS_OFFSETS or
Field.TermVector.WITH_OFFSETS